Ribbon cables contain many fibers that are embedded in a plastic material in parallel, forming a flat ribbon-like structure. Ribbon cables are used directly in friendly environments without any further protection or reinforcement. For many other applications, one or more ribbons are packaged with strength members, such as kevlar, in a PVC jacket for protection and easy handling. Such a ribbon cable 20 is illustrated in FIG. 1. The ribbon cable 20 contains two 12-fiber ribbons 22, which are formed by fibers 24 embedded in coatings 26. The 12-fiber ribbons 22 are packaged within the jacket 28 with strands 30 of strength members. The jacket 28 is a tubing of a rectangular cross section, which will be referred to as “flat” cable because the small thickness/width ratio of the cross section. Thus, ribbon cable 20 is relatively thin. Presently, almost all jacketed ribbon cables in applications are flat cables.
The ribbon cable 20 may be terminated directly with a multi-fiber connector 32, such as an MTO connector, by the termination process illustrated in FIGS. 2–4, in order to provide a flat cable assembly 34. The purpose of the illustrations in FIGS. 2–4 is to show how the ribbon cable 20 is attached to the connector 32. The details of the connector 32 assembling to the 12-fiber ribbons 22 of the ribbon cable 20 are not illustrated as they are well-known in the art. Alternatively, the ribbon cable 20 can be split into single fibers and then terminated with single fiber connectors, such as the SC type, as discussed and illustrated in U.S. Pat. No. 6,623,173, which is owned by the assignee of the present application. Techniques for single fiber cable termination are well established. The art of multi-fiber cable and termination are still evolving.
Flat cable assemblies have several disadvantages in cable routing. First, the flat cable assembly can only be bent along the flat side. Any attempt to bend the flat cable assembly in the other direction damages the ribbons. Second, when a flat cable assembly with more than one ribbon is bent in its only bendable direction, the outer ribbons are stretched and the inner ribbons are compressed. Since the ribbons are fixed to the connectors, the ribbons cannot slide along each other to reduce the stress resulting in potential ribbon damage or high attenuation. Third, the flat cable assembly has a low crush resistance since the jacket is thin and does not provide enough protection to the ribbons.
To overcome these disadvantages, round multi-fiber cables were recently introduced. One type of round multi-fiber cable 40a is illustrated in FIG. 5 and a second type of round multi-fiber cable 40b is illustrated in FIGS. 6 and 7. The round multi-fiber cable 40a contains two 24-fiber ribbons 42a and the round multi-fiber cable 40b contains two 12-fiber bundles 42b; the fibers in each bundle 42b are loosely contained by a string (not shown) wrapped in a helix along the length of the bundle 42b. Both the round multi-fiber cable 40a and the round multi-fiber cable 40b have a first jacket layer 44 and a second jacket layer 46. The strands 48 of strength members are sandwiched between the first and second jacket layers 44, 46. The double jacket construction makes the round multi-fiber cables 40a, 40b more crush resistant than flat cables. The round multi-fiber cable 40b in FIGS. 6 and 7 can be bent in any direction without causing significant strength to any particular fiber.
Although the round cable 40a in FIG. 5 is less resistant to bending than the round cable 40b in FIGS. 6 and 7, because the fibers in the round cable 40a are ribbonized, it is still much more improved in comparison to the flat cable 20, illustrated in FIG. 1. When the round cable 40a is bent in the narrow side of the ribbons 42a, the round cable 40a can roll gradually to twist the ribbons 42a inside the jackets 44, 46 to avoid the sharp bending stress in the ribbon 42a. This rolling effect is pre-built into the type of round multi-fiber cables discussed and illustrated in U.S. Pat. No. 6,295,401. In addition to these advantages, the round cables 40a, 40b have the feel of the traditional copper cables and are generally more friendly to handle and route than flat cables.
As round multi-fiber cables were only invented within the last few years, they have not been widely used in any practical application. It is believed that this is due, at least in part, because no technique has been established to terminate round multi-fiber cables to connectors. As round multi-fiber cables have two layers of jackets, they are harder to terminate. Round multi-fiber cables also cannot be attached to a connector in the same way as flat cables are attached to a connector because of at least two reasons. First, the existing connectors only accept a single jacket. Second, the connector components cannot fit over the round cable to give the required space for connector assembling.
The present invention thus provides a method of terminating a round multi-fiber cable with a connector that accepts ribbon cables in order to provide a solution to the aforementioned problems. The present invention further provides a round cable assembly which is formed by the method of the invention. Other features and advantages will become apparent upon reading the attached description of the invention, in combination with a study of the drawings.